In manufacturing of a semiconductor device, a substrate such as a semiconductor wafer is subjected to various liquid treatments (processes) such as a wet etching process, a chemical cleaning process and so on. In usual, such a liquid treatments is performed by a substrate liquid treatment apparatus including a plurality of liquid processing units and a treatment liquid supplying mechanism that supplies a chemical liquid to the liquid processing units. The treatment liquid supply mechanism includes, for example, a storage tank that stores a chemical liquid as a treatment liquid, and a circulation line through which the chemical liquid in the storage tank circulates. A plurality of branch supply lines are branched from the circulation line to allow the chemical liquid to be supplied to the respective liquid processing units through the corresponding branch supply lines. Some types of chemical liquids are reusable. For reusing such a chemical liquid, the chemical liquid having been used in the respective liquid processing units is recovered through a recovery line into the chemical liquid storage tank (see, e.g., JP2013-175552A and JP2006-080547A).
The chemical liquid does not always rush through the recovery line, and the recovery line is not always filled with the chemical liquid. Thus, after long time operation of the substrate liquid treatment apparatus, substances derived from the chemical liquid or reaction products generated through reaction between the chemical liquid and substrate surface structure forming materials are deposited or adhered on inner surfaces of piping members forming the recovery line. Such deposits or contaminants in the piping members sometimes peel off therefrom irregularly. The peeled contaminants flow into the storage tank and flows out therefrom into the circulation line. Since the circulation line is provided with a filter, particles derived from the contaminants are usually prevented from being supplied to the processing units.
However, the contaminants trapped by the filter clogs the filter. If clogging of the filter progresses, the contaminants having been trapped by the filter may be pushed out to the downstream side. In this case, product substrates may suffer from contamination beyond the allowable limit. Even if it is not the case, it may be necessary to replace or clean the filter and to clean the circulation line in order to cope with the contamination. In general, operation time management can prevent the aforementioned contamination problem. However, if a great amount of contaminants suddenly flow from the recovery line into the circulation line, the aforementioned filter trouble may occur suddenly. Stopping of the operation of the substrate liquid treatment apparatus for dealing with the trouble at an unintended timing impedes efficient use of the apparatus. Thus, in order to prevent unexpected peeling-off of a large amount of contaminants, it is desired to prevent a large amount of contaminants from being deposited on the recovery line.